Experimental analysis of the magnetic sense in the homing pigeon (Columba livia)

Abstract

The ability of homing pigeons (Columba livia) to return faithfully to their loft after displacement to distant and unfamiliar sites has fascinated people for centuries. This study sought to provide for the first time a detailed experimental analysis of the existence and mechanism of the magnetic sense in the homing pigeon (Columba livia) as well as of its use in pigeon homing. With the pigeon as a model species, it was also anticipated that a better understanding of magnetic navigation in general could be gained. In the first part of this study, a choice discrimination technique was developed in the laboratory, which required four individually-trained pigeons to discriminate between the presence and absence of a magnetic field intensity anomaly by mounting one of two available platforms in anticipation of food. The percentage of correct choices achieved was clearly above chance level thus demonstrating for the first time convincingly and reliably the existence of a magnetic sense in the homing pigeon. Secondly, the location and mechanism of the pigeon's magnetic sense was investigated through impairment of the conditioned magnetic response with a small but strong magnet as well as local anaesthesia, both applied at the suspected location of the magnetoreceptor. These experiments successfully demonstrated that the pigeon's magnetic sense is located in the nasal region and is most likely magnetite-based. Impairment through nerve sectioning showed that magnetic information is transmitted to the brain via the ophthalmic branch of the trigeminal nerve. Thirdly, the application of the same magnet during releases in the field from 26 sites located around a loft in Germany consistently and reproducibly deflected the average vanishing direction of magnet pigeons to the right of that of the control group carrying brass weights. This clearly demonstrated that pigeons use spatial information provided by the earth's magnetic field to determine their position during homing. Lastly, the analysis of control data from current and past pigeon releases revealed a strong correlation between the pigeons' initial orientation and the underlying magnetic field intensity topography at the release site, thus providing for the first time a possible explanation for the phenomenon of the release site bias. In conclusion, homing pigeons have a magnetic sense and use it to find their way home.